1. Field of the Invention
The present invention relates to an image processing apparatus for performing an optimum process with respect to an image signal acquired by scanning an original so as to reproduce this original with complete fidelity.
2. Description of the Related Art
Very recently, so-called xe2x80x9cdigital composite machinesxe2x80x9d constituted by adding scanners to printers have been actively developed. Among the presently available digital composite machines, such digital composite machines having a major object to reduce manufacturing cost thereof are normally equipped with so-called xe2x80x9clow-resolution CCD line sensorsxe2x80x9d as imaging elements of input apparatuses for scanning the above-described original. This low-resolution CCD line sensor owns low resolution on the order of 400 dpi. Also, the above-described digital composite machines can hardly employ a so-called xe2x80x9c5-set lensxe2x80x9d as the lens system of the above-described input apparatus. This 5-set lens system is usually employed in a high-class digital composite machine. This is because the component cost of this lens system would be increased in the case where the above-explained 5-set lens is employed. As a consequence, the presently developed digital composite machines have employed as the above lens system, a so-termed xe2x80x9c3-set lensxe2x80x9d capable of having a simple lens structure and also of reducing component cost.
The above-described input apparatus scans an original to produce an image signal. The resolution of the image indicated by this image signal is made equal to the resolution of the above-explained imaging element. As a result, the digital composite machine converts the resolution of this image signal into so-termed xe2x80x9chigh resolutionxe2x80x9d on the order of 600 dpi by way of a so-called xe2x80x9cASICxe2x80x9d. In the case where the digital composite machine having such an arrangement is used to scan an original so as to produce an image signal and so-called xe2x80x9c7-class charactersxe2x80x9d are written on this original, since the MTF (Modulation Transfer Function) of the above-described input apparatus is very deteriorated, there are many possibilities that the 7-class characters of the image represented by the image signal would be blurred.
FIG. 29 is a schematic block diagram for showing an arrangement of a first conventional digital composite machine 1. This first conventional digital composite machine 1 contains an imaging element 3, an A/D converter 4, an image processing apparatus 5, and an LSU 6. In FIG. 29, as a functional structure of the image processing apparatus 5, processes carried out in the image processing apparatus 5 are expressed by blocks, and a flow of an image signal is indicated by an arrow. The image is an analog signal when this image signal is outputted from the imaging element 3, namely a CCD line sensor. This analog image signal is quantized by the A/D converter 4 to become, for example, an 8-bit digital signal. The quantized image signal is supplied to the image processing apparatus 5. The image processing apparatus 5 first performs a so-called xe2x80x9cshading processxe2x80x9d 7 and a visual sensitivity correcting process 8 with respect to the quantized image signal. Next, this image processing apparatus 5 carries out both a density reversing process 9 suitable for the technical specification of the LSU 6, and a gamma converting (correcting) process 10 fitted to an output characteristic of a printer with respect to the image signal which has been processed by the visual sensitivity correcting process. Furthermore, the image processing apparatus 5 performs a resolution converting process 11 for the gamma-corrected image signal in order to convert resolution of an image indicated by this image signal in connection with the resolution of the printer. Finally, the image processing apparatus 5 performs a half tone processing operation 12 for the image signal which has been processed by the resolution converting process.
As previously explained, the first conventional digital composite machine 1 hardly perform any process for the image signal acquired from the imaging element 3 except for the processes required to fit this image signal to the technical specifications of the printer and the LSU. FIG. 30 represents an image indicated by such an image signal acquired by the digital composite machine 1 in accordance with the above-explained sequential process by scanning a test original in which a so-called xe2x80x9chalftone dot photographxe2x80x9d of 133 lines is mixed with a black solid portion and a 7-class character. A black solid portion implies such a portion composed of only by pixels which may be seen as real black by a person. It should be understood that a black-solid-displayed image portion within an image may be referred to as a black solid portion; an image portion for displaying a halftone dot photograph may be referred to as a halftone dot portion; and an image portion for displaying a character may be referred to as a character portion. As represented in FIG. 30, the 7-class character is displayed under blurring condition within this image. As previously explained, one of reasons for such blurred characters is known as follows. That is, since the input apparatus of the digital composite machine 1 designed to lower the manufacturing cost owns the deteriorated MTF, the lines cannot be printed out under clear conditions. As a consequence, in the presently available digital composite machines, this MTF may be improved due to the electronic filtering process additionally combined with a plurality of the above-explained processes.
FIG. 31 is a schematic block diagram for representing an arrangement of a second conventional digital composite machine 14 for preforming an electronic filtering process. Compared with the first conventional digital composite machine 1, this second conventional digital composite machine 14 owns a different structure that the above-explained electronic filtering process 16 is interposed between the density reversing process 9 and the gamma correcting process 10 of the functional structure employed in the image processing apparatus 15. Other structural elements of this second conventional digital composite machine 14 are identical to those of the first conventional digital composite machine 1. It should also be noted that the same reference numerals shown in the first conventional digital composite machine 1 will be employed as those for denoting the same, or similar structural elements of the second conventional digital composite machine 14, and descriptions thereof are omitted.
Referring now to FIG. 32A and FIG. 32B, a description will be made of an electronic filtering process. First, a selection is made of, as a pixel of interest 17, any one of plural pixels which constitute an image indicated by an image signal which has been processed by a density reversing process. Next, a plurality of pixels located around this interest pixel, a so-called xe2x80x9c8-near pixelxe2x80x9d are selected as peripheral pixels 18. FIG. 32A is a schematic diagram for representing a positional relationship between the pixel of interest 17 and the peripheral pixels 18. Subsequently, a corrected density xe2x80x9cImg 4*xe2x80x9d is calculated based upon the below-mentioned formula by using a density xe2x80x9cImg 4xe2x80x9d of the interest pixel 17, and also the respective densities xe2x80x9cImg 0 to Img 3xe2x80x9cand xe2x80x9cImg 5 to Img 8xe2x80x9d of the peripheral pixels 18, and furthermore, filter coefficients xe2x80x9cF0xe2x80x9d to xe2x80x9cF8xe2x80x9d of the respective pixels defined by a preset filter. FIG. 32B indicates a corresponding relationship among the interest pixel 17, the peripheral pixels 18, and the filter coefficients F0 to F8. Furthermore, the density xe2x80x9cImg 4xe2x80x9d of the interest pixel 17 is replaced by the corrected density xe2x80x9cImg 4*xe2x80x9d. The above-explained process is repeatedly performed while changing any one of the above-described pixels until all of the pixels are selected one time as the interest pixel 17. As a result, the above-explained electronic filtering process is performed for the above-explained image.                               Img          ⁢                      xe2x80x83                    ⁢          4                *=                              (                                          ∑                i                            ⁢                              (                                  Imgi                  xc3x97                  Fi                                )                                      )                    /                      (                                          ∑                i                            ⁢              Fi                        )                                              (        1        )            
The above-explained filter owns the different filter coefficients F0 to F8, depending upon the filtering purpose. For example, a filter indicated in FIG. 33 is designed so as to improve the MTF, and contains the edge enhancement component.
FIG. 34 is an image indicated by such an image signal which is produced by processing the test original explained in FIG. 30 in accordance with the above-described sequential operation by the above-described digital composite machine 14. In comparing the image of FIG. 30 with the image of FIG. 34, since the 7-class characters are emphasized in the image of FIG. 34 by additionally providing the electronic filtering process, these characters appear as being floated from the surface of this image. However, the waving pattern, namely the Moire phenomenon occurs in the halftone dot photograph portion within the image shown in FIG. 34. This Moire pattern is caused by the fact that since the edge enhancement component of the filter is strong, the arranging period of the halftone dots for constituting the halftone dot photograph may interfere with the period of the filter. Also, so-called xe2x80x9cwhite dropoutsxe2x80x9d occur in the black solid portion within the image of FIG. 34. This white dropouts problem is caused by the below-mentioned reason. That is, the difference among the densities of the plural pixels contained in the black solid portion becomes larger than the above-described difference of the pixels before being corrected, because the visual sensitivity correcting process is carried out. As a result, an inclination is produced in the curved line indicating the density distribution of the pixels contained in the black solid portion. When the above-described electronic filtering process is performed for the image by employing the filter, since the inclination of this curved line is emphasized, so-called xe2x80x9cwhite dropoutsxe2x80x9d readily occur in pixels corresponding to such an inclination portion of the curved line within the black solid portion. As previously explained, when both the characters and the halftone dot photograph are displayed on the image to be processed, it is practically difficult to achieve two objects at the same time, namely to make the characters clear, and to prevent the occurrence of the Moire phenomenon in the halftone dot photograph.
Japanese Unexamined Patent Publication JP-A 5-344339 (1993) discloses a first conventional technique in connection with making characters clear and preventing the occurrence of the Moire phenomenon. That is, the image processing apparatus described in this application owns the object to avoid the change in the overall image density caused by the edge enhancement process and also to avoid the deterioration of the image quality caused by this density change. Furthermore, this application owns another object to maintain the sharpness of the characters and the gradation characteristic of the pictorial patterns without introducing a so-called xe2x80x9carea separating processxe2x80x9d for the image. To achieve these objects, this conventional image processing apparatus performs the filtering processes for the respective density of the pixels which constitute the image by employing the calculating devices in order to edge-emphasize the image indicated by the digital image signal. Subsequently, the conventional image processing apparatus removes the outputs derived from the calculating device as the error portions, namely the overflow portion and the underflow portion of the density of each pixel which has been filtered. Furthermore, the error portion of the density of each pixel is distributed to the pixels located at the peripheral portion of each pixel.
In the case where MTF of a digital image signal to be processed is relatively better, since the strengths of the edge enhancement components of the filter used in the filter processing operation can be weakened, the above-explained image processing apparatus disclosed in the application can prevent the image quality of the filtered image from being deteriorated, and furthermore can make the characters sharp/clear. However, when the MTF of this digital image signal is not better, since the strength of the edge enhancement component of the filter must be strengthened, this conventional image processing apparatus can hardly avoid both the following problems. That is, the white dropouts occur in the black solid portion of the filtered image, and also the Moire phenomenon occurs in the halftone dot photograph.
To avoid two problems, namely the white dropouts in the black solid portion contained in the filtered image and the occurrence of the Moire phenomenon in the filtered image, the image to be processed must be correctly separated into the character portion, the black solid portion, and the halftone dot photograph portion. Then, these three image portions are required to be filtered by way of the optimum filtering means. However, when the image to be processed is correctly separated into the three image portions, since a so-called xe2x80x9carea separating processxe2x80x9d would become complex, the cost of the digital composite machine would be necessarily increased.
Japanese Unexamined Patent Publication JP-A 6-14191 (1994) discloses a second conventional technique in connection with making characters clear and preventing the occurrence of Moire phenomenon. The publication discloses a processing apparatus for improving image quality comprising a halftone dot filter. The halftone dot filter is such constructed that smoothing processing is carried out for patterns where high density pixels are arranged in a slanting direction to a scanning direction such as a halftone dot area pattern and highlighting processing is carried out for patterns where high density pixels are arranged continuously in length and width directions to the scanning direction such as a character area pattern.
The processing apparatus for improving image quality further comprises detecting means for detecting a white pixel, a contour highlighting filter and pseudo halftone processing means. The white pixel detecting means detects a white pixel from a periphery of a pixel of interest in an image to be processed. Image data is fed to the halftone dot filter and the contour highlighting filter, respectively, to be processed in parallel. When there is no detection of white pixel, an output of the halftone dot filter is fed to the pseudo halftone processing means, and when there is a detection of white pixel, an output of the contour highlighting filter is fed to the pseudo halftone processing means.
In an image forming apparatus provided with a processing apparatus for improving image quality, precision of image area separation has a large influence on the finished quality of printed matter. Such a image forming apparatus requires, in addition to a filter, a circuit for area separation and a circuit for detecting a white pixel, and therefore there is a tendency to increase the manufacturing cost.
An object of the invention is to provide an image processing apparatus capable of mitigating a Moire phenomenon and also capable of preventing an occurrence of so-called xe2x80x9cwhite dropoutsxe2x80x9d in a black solid portion of an image to be processed without carrying out an area separating process for this image, and further capable of clearly printing a relatively small character. Furthermore, another object of the present invention is to provide an image processing apparatus capable of avoiding such a problem that when the area separating process is carried out for the image to be processed and thereafter the above-described filtering process is performed for the area-separated image, even when the resultant image is erroneously separated into three image portions due to deteriorated precision of the area separating process, the erroneously separated image portion effectively appears in the filtered image.
The invention provides an image processing apparatus comprising:
area designating means for selecting any one of pixels as a pixel of interest, which are contained in an image composed of a plurality of reversed density pixels, to thereby designate as an area to be processed, an area contained in said image which is composed of a predetermined number of pixels including the pixel of interest;
average value calculating means for performing a weighted average calculation of density of all of the pixels within the area to be processed by employing a plurality of weighting coefficients corresponding to a positional relationship between each of the all pixels and the pixel of interest so as to thereby calculate weighted average values of the density of all of the pixels;
limiting means for limiting the weighted average values to be smaller than, or equal to a predetermined upper limit density and to be larger than, or equal to a predetermined lower limit density;
first comparing means for comparing the weighted average value limited by the limiting means with the density of the interest pixel; and
density replacing means for replacing the density of the interest pixel by the weighted average value when the density of the interest pixel is less than the limited weighted average value, and also for maintaining the density of the interest pixel when the density of the interest pixel is more than, or equal to the limited weighted average value, in response to the comparison result of the first comparing means.
According to the invention, the image processing apparatus first calculates the above-described weighted average value which is limited. This weighted average value corresponds to the corrected density of the interest pixel when the conventional so-called filtering process has been performed for the image. Next, the image processing apparatus compares the weighted average value with the density of the interest pixel, and then corrects the density of the interest pixel based upon the comparison result in the above-explained manner. When all of the pixels contained in the image are selected as the pixels of interest to be processed by way of the above-explained process, the electronic filtering process featured by the present invention may be carried out for the above-described image. As a result, the corrected density of the interest pixel is always higher than, or equal to the density of this interest pixel before being corrected, but is not lower than the density of the interest pixel before being corrected. In other words, the corrected pixel of interest becomes darker than the interest pixel before being corrected.
For example, it is now assumed that the image to be processed is blurred, and furthermore, a small character made of a so-called xe2x80x9c7-class characterxe2x80x9d, a black solid portion, and a halftone dot photograph are represented on this image. In the case where the image is processed by employing the image processing apparatus according to the invention, the character can be made clear, and the Moire phenomenon occurred in an image portion of the image on which the halftone dot photograph is displayed can be reduced, as compared with the image which is processed by the conventional filtering process. Moreover, it is possible to prevent the occurrence of so-called xe2x80x9cwhite dropoutsxe2x80x9d in the black solid portion of the image.
In the invention it is preferable that the image processing apparatus further comprises:
second comparing means for comparing the density of the interest pixel with a predetermined reference density; and
the density replacing means further replaces the density of the interest pixel by the limited weighted average value in the case where the density of the interest pixel is less than the reference density in response to the comparison result obtained from the second comparing means.
According to the invention, the image processing apparatus is arranged by employing the above-described arrangement. As a consequence, when the density of this interest pixel before being corrected is lower than the reference density, the image processing apparatus replaces the density of the interest pixel by the weighted average value irrespective of such a large/small relationship between the density of this interest pixel before being corrected and the limited weighted average value. As a result, when the density of the interest pixel before being corrected is higher than, or equal to the reference density, the corrected interest pixel does not become brighter than the interest pixel before being corrected. However, there are some possibilities that when the density of the interest pixel before being corrected is lower than the reference density, the corrected interest pixel becomes brighter than the interest pixel before being corrected. In other words, when the density of the interest pixel before being corrected is lower than the reference density, this image processing apparatus carries out the conventional filter processing operation. As previously explained, this image processing apparatus properly selects the filtering process as explained above and the conventional filtering process in response to the large/small relationship between the reference density and the density of the interest pixel before being corrected.
For example, it is now assumed that the image to be processed is blurred, and furthermore, a small character made of a so-called xe2x80x9c7-class characterxe2x80x9d, a black solid portion, and a halftone dot photograph are represented on this image. In the case where the image is processed by employing the image processing apparatus according to the invention, the filtering process is carried out for a line of a character, a black solid portion, and a halftone dot photograph with a high density such as a 133-line point photograph, contained in this image. The conventional filtering process is carried out for the remaining portion of this image by the image processing apparatus of the invention. As a result, the image processing apparatus of the invention can more clearly display the character, and can prevent the so-called xe2x80x9cwhite dropoutsxe2x80x9d in the black solid portion within the image. Moreover, this image processing apparatus can firmly prevent the occurrence of the Moire phenomenon in the halftone dot photograph with a high density such as the 133-line point photograph; when the enhancement filtering process is carried out, the Moire phenomenon can readily occur in this 133-line point photograph. Since the conventional filtering process is performed for the halftone dot photograph with a low density such as a 65-line point photograph, the resultant image can be clearly displayed.
In the invention it is preferable that the image processing apparatus further comprises:
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area; and for setting the reference density used in the second comparing means in response to the selected area,
the reference density which is set when the character area is selected is made higher than the reference density which is set when the photograph area is selected, and
also the reference density which is set when the photograph area is selected is made higher than he reference density which is set when the halftone dot area is selected.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As a consequence, the reference density is varied, depending upon such a condition as to whether or not the pixel of interest is included in any one of the character area, the halftone dot area, and the photograph area. The image processing apparatus according to the invention performs the filtering process as explained above for the image to be processed by employing the predetermined reference density. Assuming now that a small character having a so-called xe2x80x9c7-class characterxe2x80x9d, a black solid portion, and a halftone dot photograph area represented on the image, when the image processing apparatus according to the invention processes this image, the reference density defined when the pixel of interest is contained in the photograph area is made lower than the reference density defined when the pixel of interest is included in the character area. As a result, in the processed image, the gradation characteristic of the image portion which is composed of the pixels, the density of which before being corrected is relatively low, can be maintained, similar to the photograph area. Also, as a result, the character contained, in the processed image can be made sharp, the Moire phenomenon occurred in the halftone dot photograph portion within the image can be reduced. Moreover, the white dropouts in the black solid portion within the image can be avoided.
In the invention it is preferable that the image processing apparatus comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original; and
reference density setting means for setting the reference density used in the second comparing means in response to the ratio, and
the higher the ratio becomes, the higher the reference density is set.
According to the invention, the image processing apparatus is realized by employing the above-explained arrangement. As a result, in response to the above-described ratio, namely either a so-called xe2x80x9cenlarging ratioxe2x80x9d or a so-termed xe2x80x9creducing ratioxe2x80x9d, the reference density is varied. This reason is given as follows. The larger this ratio becomes, namely the larger the image is enlarged, the stronger the image is blurred when this image is produced by the image producing means. As a consequence, if the conventional filtering process rather than the filtering process as explained above is carried out for such an image produced when the ratio is set to be a large value, then the image quality of the filter-processed image can be improved. On the other hand, when the ratio is set to be a small value, namely when the image is reduced, the blurring degree of the image produced from the image producing means is lower than that of the enlarged image. As a consequence, if the filtering process as explained above is carried out for such an image obtained when the ratio is set to be a small value, then the image quality of the processed image can be improved. As apparent from the foregoing descriptions, as previously explained, the image processing apparatus of the invention can properly select the filtering process in accordance with the ratio while varying the reference density in response to the ratio. As a consequence, the image quality of the processed image can become the optimum image quality in accordance with the ratio.
In the invention it is preferable that the image processing apparatus further comprises:
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined photograph mode for processing a photograph original; and
reference density setting means for setting the reference density used in the second comparing means in response to the designated mode, and
the reference density set when the character mode is designated is made higher than the reference density set when the photograph mode is designated.
According to the invention, the image processing apparatus is realized by the above-described arrangement. For example, the character mode and the photograph mode are designated by the operator, depending upon such a condition as to whether an original having a large number of characters, or another original having a large number of photographic portions is represented on the image to be processed. The reference density is varied in response to the designated mode. This reason is given as follows. When the character mode rather than the photograph mode is selected, the filtering effect of the filtering process as explained in the above is made stronger. As a result, it can be expected that the image quality of the processed image can be furthermore improved. Under such a circumstance, since the image processing apparatus of the invention varies the reference density in response to the designated mode, the effect of the filtering process is changed in response to the designated mode. As a result, the image quality of the processed image can become optimum image quality suitable for the designated mode.
In the invention it is preferable that the image processing apparatus further comprises:
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined mixed original mode for processing an image on which both a character and photograph are photographed; and
reference density setting means for setting the reference density used in the second comparing means in responses to the designated mode, and
the reference density set when the character mode is designated is made higher than the reference density set when the mixed original mode is designated.
According to the invention, the image processing apparatus is realized by the above-described arrangement. For example, the character mode and the mixed original mode are designated by the operator, depending upon such a condition as to whether an original having large number of characters, or another original having a 50-to-50 percent of photographic/character portions is represented on the image to be processed. Under such a circumstance, since the image processing apparatus of the invention varies the reference density in response to the designated mode, the effect of the filtering process is changed in response to the designated mode. As a result, the image quality of the processed image can become an optimum image quality suitable for the designated mode.
In the invention it is preferable that this image processing apparatus further comprises:
mode designating means for designating any one of a predetermined mixed original mode for processing an image on which both a character and a photograph are photographed, and a predetermined photograph mode for processing a photograph original; and
reference density setting means for setting the reference density used in the second comparing means in response to the designated mode, and
the reference density set when the mixed original mode is designated is made higher than the reference density set when the photograph mode is designated.
According to the invention, the image processing apparatus is realized by the above-described arrangement. For example, the mixed original mode and the photograph mode are designated by the operator, depending upon such a condition as to whether both the character and the photograph are displayed on the image to be processed in a better balance, or the photograph is mainly displayed on this image to be processed. Under such a circumstance, since the image processing apparatus of the invention varies the reference density in response to the designated mode, the effect of the filtering process is changed in response to the designated mode. As a result, the image quality of the processed image can become an optimum image quality suitable for the designated mode.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
reference density setting means for selecting any one area containing the pixel of interest from the character area, the halftone dot area, and the photograph area, and also for setting the reference density used by the second comparing means in response to the selected area and the selected ratio,
the higher the ratio becomes, the higher the reference density is set; the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected, and
the reference density set when the photograph area is selected is made higher than the reference density set when the halftone dot area is selected.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As a consequence, in the image processing apparatus the filtering process as explained above is carried out for the image to be processed by employing the reference density determined based upon both the area containing the interest pixel and the ratio. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-described two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined photograph mode for processing a photograph original; and
reference density setting means for setting the reference density employed in the second comparing means in response to the designated mode and the ratio,
the higher the ratio becomes, the higher the reference density is set; and the reference density set when the character mode is designated is made higher than the reference density set when the photograph mode is designated.
According to the invention, the image processing apparatus is realized by employing in the above-described arrangement. As a consequence, in the image processing apparatus the filtering process as explained above is carried out for the image to be processed by employing the reference density determined based upon both the ratio and the designated mode. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-described two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined mixed original mode for processing an image on which both a character and photograph are photographed; and
reference density setting means for setting the reference density used by the second comparing means in response to the designated mode and the ratio, and
the higher the ratio becomes, the higher the reference density is set; and the reference density set when the character mode is designated is made higher than the reference density set when the mixed original mode is selected.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As consequence, in the image processing apparatus the filtering process as explained above is carried out for the image to be processed by employing the reference density determined based upon both the designated mode and the ratio. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-described two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
mode designating means for designating any one of a predetermined mixed original mode for processing an image on which both a character and a photograph are photographed, and a predetermined photograph mode for processing a photograph original; and
reference density setting means for setting the reference density used by the second comparing means in response to the designated mode and the ratio,
the higher the ratio becomes, the higher the reference density is set, and
the reference density set when the mixed original mode is designated is made higher than the reference density set when the photograph mode is designated.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As a consequence, in the image processing apparatus the filtering process as explained above is carried out for the image to be processed by employing the reference density determined based upon both the designated mode and the ratio. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-described two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined photograph mode for processing a photograph original; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area; and for setting the reference density used in the second comparing means in response to the selected area and the designated mode,
the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected; the reference density set when the halftone dot area is selected is made higher than the reference density set when the photograph area is selected, and
also the reference density set when the character mode is designated is made higher than the reference density set when the photograph mode is designated.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As a consequence, in the above-explained image processing apparatus the filtering process as described above is carried out for the image to be processed by using the reference density determined based upon the area containing the interest pixel and the designated mode. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-explained two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined mixed original mode for processing an image on which both a character and photograph are photographed; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area; and for setting the reference density used in the second comparing means in response to the selected area and the designated mode,
the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected; the reference density set when the halftone dot area is selected is made higher than the reference density set when the photograph area is selected, and
also the reference density set when the character mode is designated is made higher than the reference density set when the mixed original mode is designated.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As a consequence, in the above-explained image processing apparatus the filtering process as described above is carried out for the image to be processed by using the reference density determined based upon the area containing the interest pixel and the designated mode. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-explained two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
mode designating means for designating any one of a predetermined mixed original mode for processing an image on which both a character and a photograph are photographed, and a predetermined photograph mode for processing a photograph original; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area, and for setting the reference density used in the second comparing means in response to the selected area and the designated mode,
the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected; the reference density set when the halftone dot area is selected is made higher than the reference density set when the photograph area is selected, and
also the reference density set when the mixed original mode is designated is made higher than the reference density set when the photograph mode is designated.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. As a consequence, in the above-explained image processing apparatus the filtering process as described above is carried out for the image to be processed by using the reference density determined based upon the area containing the interest pixel and the designated mode. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-explained two conditions.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined photograph mode for processing a photograph original; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area, and for setting the reference density used in the second comparing means in response to the selected area, the designated mode, and the ratio,
the higher the ratio becomes, the higher the reference density is set; the reference density set when the character mode is designated is made higher than the reference density set when the photograph area is designated,
the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected, and
also the reference density set when the halftone dot area is selected is made higher than the reference density set when the photograph mode is selected.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. Accordingly, the reference density is varied in response to the ratio, the area containing the interest pixel, and the designated mode. As a consequence, in the above-explained image processing apparatus the filtering process as described above is carried out by using the reference density determined in this manner. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-explained three conditions.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
mode designating means for designating any one of a predetermined character mode for processing a character original and a predetermined mixed original mode for processing an image on which both a character and photograph are photographed; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area; and for setting the reference density used in the second comparing means in response to the selected area, the designated mode, and the ratio,
the higher the ratio becomes, the higher the reference density is set; the reference density set when the character mode is designated is made higher than the reference density set when the mixed original mode is designated,
the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected, and
also the reference density set when the halftone dot area is selected is made higher than the reference density set when the photograph mode is selected; and further the reference density set when the halftone dot area is selected is made higher than the reference density set when the photograph area is selected.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. Accordingly, the reference density is varied in response to the ratio, the area containing the interest pixel, and the designated mode. As a consequence, in the above-explained image processing apparatus the filtering process as described above is carried out by using the reference density determined in this manner. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-explained three conditions.
In the invention it is preferable that the image processing apparatus further comprises:
image producing means for producing the image by scanning a surface of an original to be processed, and for varying a ratio of a dimension of the image to the original;
separating means for separating the image to be processed into a character area for photographing a character, a halftone dot area for photographing a dotted picture represented by using a half tone image method, and a photograph area for photographing a photograph composed of pixels having gradation; and
mode designating means for designating any one of a predetermined mixed original mode for processing an image on which both a character and a photograph are photographed, and a predetermined photograph mode for processing a photograph original; and
reference density setting means for selecting any one area in which the pixel of interest is included, from the character area, the halftone dot area, and the photograph area, and for setting the reference density used in the second comparing means in response to the selected area, the designated mode, and the ratio,
the higher the ratio becomes, the higher the reference density is set; the reference density set when the mixed original mode is designated is made higher than the reference density set when the photograph mode is designated,
the reference density set when the character area is selected is made higher than the reference density set when the photograph area is selected, and
also the reference density set when the halftone dot area is selected is made higher than he reference density set when the photograph area is selected.
According to the invention, the image processing apparatus is realized by employing the above-described arrangement. Accordingly, the reference density is varied in response to the ratio, the area containing the interest pixel, and the designated mode. As a consequence, in the above-explained image processing apparatus the filtering process as described above is carried out by using the reference density determined in this manner. As a result, the image quality of the processed image can become an optimum image quality suitable for the above-explained three conditions.
In the invention it is preferable that
colors of the respective pixels of the image are defined based on the density, the saturation, and the hue; and
the average value calculating means, the first comparing means, and the density replacing means are carried out with respect to the density.
According to the invention, the image processing apparatus is operated in the above-explained manner when the image to be processed is a so-called xe2x80x9ccolor imagexe2x80x9d. As a result, the image processing apparatus of the invention can reduce the Moire phenomenon caused by the filtering process, and at the same time, can avoid the white dropouts occurred in the black solid portion contained in the image by employing the apparatus equipped with the relatively low cost structure.
As previously described, in accordance with the present invention, the image processing apparatus first calculates the weighted avenge value of the density of the interest pixel by executing the filtering process identical to the conventional filtering process. Only when the corrected density is lower than the density of this interest pixel before being corrected, this image processing apparatus replaces the density of the interest pixel before being processed by the weighted average value. As a consequence, in the image processed by the above image processing apparatus, the character can be made sharp, and furthermore, the Moire phenomenon occurred in the image portion for displaying the halftone dot photograph can be reduced. Furthermore, it is possible to avoid the occurrence of so-called xe2x80x9cwhite dropoutsxe2x80x9d in the black solid portion contained in the above-described image.
Also, according to the present invention, the image processing apparatus further compares the density of the interest pixel before being corrected with predetermined reference density. In the case where the density of this interest pixel before being corrected is lower than the reference density, the image processing apparatus replaces the corrected density of this interest pixel by the weighted average value. As a consequence, in the image processed by the above image processing apparatus, the character can further be made sharp, and furthermore, the Moire phenomenon occurred in the image portion for displaying the halftone dot photograph can be reduced. Furthermore, it is possible to avoid the occurrence of so-called xe2x80x9cwhite dropoutsxe2x80x9d in the black solid portion contained in the above-described image.
Furthermore, according to the present invention, the above-explained image processing apparatus sets the reference density in response to at least one of the ratio of the original to the image to be processed, the mode corresponding to the original, and the feature amount of the area within the image where the interest pixel is included. As a result, the image processing apparatus can optimize the image quality of the processed image in accordance with at least one condition employed to set the reference density among the three conditions.
Also, according to the present invention, the above-described image processing apparatus performs the above-explained filtering process with respect to the density for the three elements used to define the colors of the pixel in such a case as the image to be processed is the color image. As a consequence, even when the image to be processed is the color image, the above-explained image processing apparatus can reduce the Moire phenomenon caused by correcting the density of the pixel, and at the same time, can avoid the occurrence of the white dropouts in the black solid portion within the image.